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Atomic nucleus excited with laser: A breakthrough after decades

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Re: Atomic nucleus excited with laser: A breakthrough after decades

#191

Post by airstrike »

thehappypm wrote: post #184
airstrike wrote: post #121

Earlier quoted context omitted.

> I will use the term "soccer" for the most common football of Europe, "Association football", and "football" for American football. I appreciate your valiant efforts but to my mind this is extra confusing because "soccer" is short for "association football" Time to rename American Football to "handegg" once and for all. Ok, ok, I'll settle for "American Rugby"

I've heard "handegg" before but a football is not shaped like an egg, it's vaguely egg-like but the teardrop shape of an egg is distinctly not what a football looks like.

It looks more like an egg than it looks like a ball, so if we have to force fit into a common word, my vote goes for egg

Re: Atomic nucleus excited with laser: A breakthrough after decades

#193

Post by karma_pharmer »

nullc wrote: post #189
karma_pharmer wrote: post #56

Earlier quoted context omitted.

> PS: Are you sure it's gamma emission? That takes more energy than the exciting UV photon. Apparently it is neither: Decay of the 229Th isomeric state of the neutral thorium atom occurs predominantly by internal conversion (IC) with emission of an electron https://www.nature.com/articles/nature17669 https://en.wikipedia.org/wiki/Internal_conversion This is pretty weird. You shine UV light (with exactly the right wav…

Apparently in some ionized states it can't produce the electron and will instead produce the gamma, I'm unclear where the extra energy comes from. > Almost like an exponentially-discharging solar-powered current source (for a very specific wavelength of "solar"). If one could make the UV source highly efficient perhaps it could be used as a battery with extremely good energy density.

I'm unclear where the extra energy comes from.

When the atom ejects an electron, the hole left behind gets filled by an electron from a neighboring atom. Then the same thing happens to the neighbor -- and so on. This is electrical current flowing. Eventually the loop closes and some hole somewhere in the universe gets filled by the original ejected electron.

The hole in one atom can get filled by an electron from a higher orbital in a neighboring atom. In that case the energy gained will be greater than the energy lost by the original electron ejection. This is the situation where you get a photon (x-ray) with a higher energy (= shorter wavelength) than the original incident photon (ultraviolet).

Of course there's no free lunch. The way this happens is that N thorium atoms eject electrons from some orbital with energy X, the electrons shuffle around, and those N holes get filled by donors from orbitals whose total energy is N*X even though some of the donors are at higher levels and some are at lower levels.

If one could make the UV source highly efficient perhaps it could be used as a battery with extremely good energy density.

Yeah I've been thinking that if we had really tiny VLSI-integrated UV lasers (which we absolutely don't, not even close) that a bunch of these 229Th atoms embedded in a silicon chip would be a device with totally fascinating properties.

We can build waveguides in silicon wafer processes pretty easily but I'm not sure we can do that at UV wavelengths. You could imagine a single, big, off-chip laser whose beam can be steered by waveguides to illuminate any of a few billion 229Th deposits. These could act like the configuration memory bits of an FPGA. They would be "almost nonvolatile" -- you'd have to refresh them every hour or so, instead of several thousand times per second (dram) or never (sram). At such a low refresh rate the steering doesn't need to be particularly fast, and having to share one laser across all the deposits would not be a problem.

Unfortunately 229Th is mildly radioactive, but so are household smoke detectors so hopefully people wouldn't freak out about this.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#194

Post by _carbyau_ »

tzs wrote: post #119
thebruce87m wrote: post #65

American football or European football? This is like the gallon thing all over again.

Note: I will use the term "soccer" for the most common football of Europe, "Association football", and "football" for American football. And before anyone says that soccer fields should be called "pitches" not "fields" I will note that FIFA's "Laws of the Game" call it "field" 184 times. They only mention "pitch" in the glossary where the heading for "field" is "Field of play (pitch)". Generally you want to use Ameri…

I mean, you want a classically beautiful field right. So use the Golden Ratio.

Of the English Premier League fields Brentford is pretty close: 105/1.618 = 64.89; close enough to their 105x65m field.

Honestly I'd settle on a 100m length though. Thus a 100x61.8 field.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#195

Post by noqc »

lifeisstillgood wrote: post #51

>>> For example, the Earth's gravitational field could be analyzed so precisely that it could provide indications of mineral resources Hold on how does that work? I have had a sort of sci-fi idea that sufficiently sensitive gravitational field measurements coukd detect the passing of submarines (I am not sure on the maths tbh) - which would render a lot of nuclear strategy moot. Just need to get a grasp on the maths

Submarines are basically exactly the same mass as the water they displace.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#196

Post by cyanydeez »

JanisErdmanis wrote: post #177
blincoln wrote: post #161

Earlier quoted context omitted.

Since mining is only concerned with material that's within maybe 0.1% of the distance from the surface to the core, seems like you'd just need to move the sensor around and make sure the signal changes about where you'd expect for a mass of X Kg at a depth of Y meters instead of a supermassive chunk of dense material much deeper. Or, to put it another way, build a grid map of the area and subtract any background sign…

In practice, that's what would happen. Move around until seeing some larger gravitational pull, likely indicating some deposit. However, formally, this is not correct due to the mere fact that the gravitational force is proportional to 1/R^2, just like a Columb force. Thus, there are infinite numbers of mass distributions that produce the exact same gravitational field on the surface. The planet could be hollow, and…

Thats why you generate typical geologic formations and add a few drillhole constraints.

Sure this isnt going to be a star trek scanner but for practical purposes theres a bunch of other techniques to constrain the results

Re: Atomic nucleus excited with laser: A breakthrough after decades

#197

Post by smaddox »

ChrisClark wrote: post #154
andrewflnr wrote: post #143

Earlier quoted context omitted.

Where do electron transitions usually dump excess energy?

Don't they usually create a photon with that energy?

For free atoms, yes. For atoms in a crystal lattice (or other solid), it's quite common for electrons to decay through phonon interactions, i.e. by emitting vibrations (i.e. heat) to the lattice.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#198

Post by smaddox »

femto wrote: post #77

An obvious question is whether this be used to build a nuclear analogue of a laser, using nuclear transitions instead of electron transitions. It turns out to have already been asked: https://physics.stackexchange.com/questions/296237/nuclear-t... In summary, the answer seems to be "maybe, but why?". The laser was originally called "a solution in search of a problem", which would suggest that "why" isn't really a rea…

To build a laser, you would need at least three energy levels, and ideally four, with particular constraints in the transition probabilties so that you can create population inversion. And you would need to pump it with a higher-energy (shorter wavelength) laser.

Perhaps doable with a free electron laser, but probably not with traditional lasers, due to the energies involved.

But, yeah, not sure what the use would be. Maybe a form of lidar that allowed measuring speed of objects to extreme precision, by measuring the dopler shift of reflected light? (Assuming light at such a short wavelength is reflected sufficiently, which it probably wouldn't be).

If there happened to be one atom/matrix that could be tuned to the transition energy of another atom's fission transition energy, then you could use it to burn nuclear material / waste. But you could just do that with the pump laser directly.

I suppose you could maybe pump such a laser with a very high temperature plasma (like fusion temperatures hot), rather than with a free electron laser. Then maybe it might make more sense.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#200

Post by was_a_dev »

bawana wrote: post #188
nullc wrote: post #24

Now how the heck do you generate ~148.38nm light with a narrow linewidth? Their approach using four-wave mixing inherently results in short pulses. .. and given that it decays through gamma emission, does this mean we could now build an optically pumped gamma ray laser?

What i was wondering…exactly… how do you make this kind of a laser? And imagine an xray laser… you could fry the guidance system of drone very precisely

Here, it appears they have used Four Wave Mixing in Xeon gas

https://en.wikipedia.org/wiki/Four-wave_mixing

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